Embodiments of the multistage centrifugal pump with integral abrasion-resistant axial thrust bearings relates generally to the field of downhole turbomachines, and more particularly to multistage centrifugal pump that includes integral axial thrust bearings.
Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, a submersible pumping system includes a number of components, including an electric motor coupled to one or more high performance pump assemblies. Production tubing is connected to the pump assemblies to deliver the petroleum fluids from the subterranean reservoir to a storage facility on the surface. The pump assemblies often employ axially and centrifugally oriented multi-stage turbomachines.
Most downhole turbomachines include one or more impeller and diffuser combinations, commonly referred to as “stages.” The impellers rotate within adjacent stationary diffusers. A shaft keyed only to the impellers transfers mechanical energy from the motor. During use, the rotating impeller imparts kinetic energy to the fluid. A portion of the kinetic energy is converted to pressure as the fluid passes through the downstream diffuser.
During operation, each impeller generates thrust in an upward or downward direction. “Up-thrust” occurs as fluid moving through the impeller pushes the impeller upward. “Down-thrust” occurs when the force imparted by the impeller to the fluid creates a reactive downward force. All multistage centrifugal pumps have a single flow rate equilibrium point where the up-thrust and down-thrust generated by the impellers are balanced. Operating the pump at flow rate outside the equilibrium point causes the up-thrust and down-thrust forces to become unbalanced. Lower flow rates cause excess down-thrust, while higher flow rates may cause excess up-thrust. To avoid these out-of-balance forces, the pump is provided with a narrow operating range.
In the past, large thrust-bearings have been used to control the aggregated thrust load from the entire impeller stack. Large thrust bearings are complicated to manufacture and wear over time. To be effective, the large thrust bearings and turbomachinery stages must be accurately shimmed and balanced to properly place the thrust loads at the thrust bearing.